It didn’t take long after the December elementary school shooting in Newtown, Conn., for the debate to evolve into one pitting the First Amendment against the Second Amendment.

Lobbyists for gun owners and manufacturers blamed violent content in the media as they sought to contain the public outcry for new restrictions on firearms.

Now, with a Senate bill calling for a deeper examination of a possible link between real-life gun violence and depictions in movies and video games, many content providers are banding together in a new campaign.

But the video game lobby is conspicuously absent.

Sources say the industry’s chief lobby, the Entertainment Software Association, is putting the final touches on a campaign of its own that it will unveil this month. Like the movie, TV and cable industries, the video game group plans to tout parental controls and will make sure the public — and, more importantly, Congress — knows that it’s doing something to keep mature games from underage buyers.

Former Sen. Gordon H. Smith, R-Ore., who runs the National Association of Broadcasters, said in an interview last week that the video game industry “would be welcome” in the content-provider coalition.

That effort is bringing together groups that are sometimes at odds with one another. In addition to the NAB, the “cable guys” at the National Cable & Telecommunications Association and the American Cable Association have signed on. The Motion Picture Association of America spearheaded the campaign, which also includes support from the National Association of Theatre Owners, DirecTV and Verizon FiOS.

Former Sen. Christopher J. Dodd, D-Conn., chairman and CEO of the MPAA, said in a statement that his member studios “are committed to not only creating some of the best movies and television in the world, but also to ensuring that parents are aware of what’s in those movies and shows.”

“It is unrealistic to assume that overworked and stressed parents can prevent their kids from viewing inappropriate content,” he said in a statement. “I believe that the only real solution is for the entertainment industry to reduce the often obscene levels of violence in the products they sell.”

His bill, if passed, would require the National Academy of Sciences to study whether video games have a unique effect on children because of the games’ “interactive nature and the personal and vivid way violence is portrayed,” according to a press release from Rockefeller’s office.

The video game industry maintains that previous research has found no connection between entertainment and real-life violence.

Smith said the coalition’s newly launched campaign follows up on entertainment industry meetings with lawmakers and Vice President Joseph R. Biden Jr., who is chairman of the Obama administration’s task force to prevent gun violence.

In addition to running ads reminding parents of the controls they have to monitor their kids’ TV consumption, Smith said the broadcasters are developing a new spot with the Ad Council that deals with mental-illness awareness.

“When I was in Congress, one of my passions was mental health, and I think that is an area where television and movies can do a great deal to inform,” he said. The ads, he said, will help people identify signs of mental illness.

“The thread that runs through all gun tragedies is mental health,” Smith added. “These are afflictions that can be highly lethal.”

The former senator wouldn’t take a position on gun control proposals, though the National Rifle Association’s executives have put the blame for mass shootings, in part, on violent media content.

“They may be throwing us under the bus, but I’m not throwing them under the bus,” Smith said. “A lot of broadcasters like me believe in the Second Amendment.”